There is a continuing trend in health care to significantly reduce and replace in-patient hospital care with ambulatory care. For example, ambulatory surgery now accounts for over 60% of all operations performed in the United States, and is expected to increase to 80% of all procedures by the year 2000. This trend is likely to continue as surgeons embrace the ongoing development of minimally invasive surgical techniques, as third party payers reduce or restrict payments for health care, and as the acceptance by patients and society grows for ambulatory care.
The traditional delivery of anesthesia for in-patient hospital care typically relies heavily on the use of inhalation anesthesia agents. For example, the Excel series anesthesia systems from Ohmeda include a hypoxic guard, sophisticated electronic ventilation, flow management systems, vaporization and breathing circuits. The systems offer a choice of monitors, vaporizers, ventilators, and offer drawers or shelves for storage. Unfortunately, the bulkiness of even advanced conventional inhalation equipment severely hinders the portability of the equipment and thereby limits the possible locations where the equipment may be used.
Another significant shortcoming for traditional inhalation anesthesia systems is that scavenging or ventilation systems are required by various governmental regulations, such as OSHA regulations in the United States. In other terms, complicated and expensive room ventilation as in a traditional operating theater is needed for conventional inhalation systems to comply with various regulations.
As reported in the March 1997 issue of Anesthesiology News, "[t]he transition from the hospital to the free-standing surgical center to the office surgical suite continues to escalate." Accordingly, the ambulatory trend in health care creates new geographic sites that may be desirably served by an unburdened anesthesia delivery system.
There are several anesthesia techniques which do not necessarily require the use of vaporized inhalants. Total intravenous infusion anesthesia (TIVA) uses liquid intravenous agents in place of the conventional vaporized inhalants. Along these lines, target controlled infusion (TCI) is a way of administering an intravenous anesthesia agent using a computer to monitor the patient and control an infusion pump. Using a computer with a pharmacokinetic program permits control of a desired plasma concentration of an agent, such as propofol, without overshooting the desired level.
Unfortunately, conventional intravenous agents for TIVA or TCI may have relatively long offset times, that is, relatively long times before the anesthesia and other effects wear off in the patient. Some agents may result in active metabolites that additionally remain for a relatively long time after stopping delivery of the anesthesia. Moreover, a quick onset and quick offset analgesia agent has not been previously available. In view of the prior shortcomings of conventional TIVA agents, there has been no incentive to develop efficient integrated platforms for using TIVA or TCI in an ambulatory setting.